Heretofore, there have been proposed various polyazo dyes for writing or ink-jet printing onto materials to be recorded such as papers, or for dyeing fibers or papers. A number of polyazo dyes are substantive, so that a dyeing process using the polyazo dyes is simple, as well as fastness of the polyazo dyes is comparatively good. The polyazo dyes having such an advantage are widely used in the art.
However, the polyazo dye has a problem to be solved. The first problem is chemical properties. Excellent chemical properties (e.g., stable solubility, stability with time of dyed density, light-resistance, etc.) are particularly required for the dye which is used as ink for writing implements. The second problem is safety. Safety of chemical substances is a great concern in recent years, so that dyes having excellent safety which have no harmful effect on the human body are required.
As the dyes having improved dyeability and fastness, for example, there have widely been used black trisazo dye or polyazo dye derived from benzidine or its derivatives (e.g., C.I. Direct Black 19, C.I. Direct Black 154, C.I. Direct Black 168, etc.) for the above applications. However, these dyes are inferior in safety to the human body because the results of AMES test of the dyes shows false positive or positive.
On the other hand, as the polyazo black dyes having improved safety to the human body, there have been used a food pigment (e.g., Food Black 2, etc.), a recording solution using the same as a recording agent, a 4,4'-diaminodiphenylamine-2-sulfonic acid based trisazo dye instead of a benzidine based one, a stilbenic tetrakisazo dye free of amino group in its molecule. However, an aqueous ink composition using these dyes provides poor water resistance and poor light-resistance in the handwriting and is inferior in dyeability and fastness.
A water-soluble dye is usually separated from an aqueous phase by means such as acid separation, salting-out and the like. However, since inorganic salts are included in the course of such separation means, it is difficult to obtain a highly pure dye and various problems due to impurities may be arisen. For example, when a low-purity dye is used as aqueous ink for writing implements, continuous replenishing of ink to the penpoint may be interfered. Also, when such a low-purity dye is used as ink for ink-jet recording, an orifice of the apparatus may be clogged.